The present invention relates broadly to a search radar apparatus, and in particular to improved search detection channels for search radar using a monopulse antenna.
The state of the art of search radar apparatus using monopulse antennas is well represented and alleviated to some degree by the prior art apparatus and approaches which are contained in the following U.S. Patents:
U.S. Pat. No. 4,334,224 issued to Gordon on June 8, 1982;
U.S. Pat. No. 4,568,940 issued to Diamond on Feb. 4, 1986; and
U.S. Pat. No. 4,739,327 issued to Konig et al on Apr. 19, 1988.
The Gordon patent discloses a secondary surveillance radar which is arranged to monitor the relative amplitudes of sum signals and difference signals that are received from a target in response to interrogations. Only those sum signals for which the sum signal exceeds the difference signal by a predetermined amplitude are accepted as valid to avoid degradation of the performance of the radar.
The Diamond patent is directed to dual-mode radar receiver that processes sum and difference signals which are generated from received radar signals to provide target angle information in terms of amplitude or phase.
The Konig et al patent describes the method and the apparatus for suppressing rain echoes in a terrain tracking radar with elevation monopulse devices. The signal in the difference channel is amplified by a predetermined factor and compared with the level of the sum signal to determine the presence of a ground echo or a rain echo.
In the prior art, it was the practice in search radars using monopulse antennas and having sum and difference beams, to perform the search function using the sum beam alone, and to employ the difference beam(s) only to obtain angle data on detected targets. The novel concept of the present invention is to provide search detection channels for both the sum and the difference beam(s) on receive, while using the sum beam for transmit as usual. This new approach extends the angular coverage of the antenna, typically by approximately twenty-five percent.